The present application relates to a semiconductor structure and a method of forming the same. More particularly, the present application relates to a semiconductor structure in which a void-free metallization structure is located on a surface of a reflow enhancement layer and a method of forming such a semiconductor structure.
As the dimensions of semiconductor devices including, for example, middle-of-the-line (MOL) contacts, are scaled down, the currently used tungsten (W) metallization scheme will not be able to meet the resistance targets for future technology nodes. This high resistance for tungsten is a result of the need for utilizing thick diffusion barrier liners and poor tungsten gap fill.
Cobalt (Co) provides an alternative to tungsten fill for MOL contacts, and is typically performed by chemical vapor deposition (CVD) to fill the groundrule features followed by a physical vapor deposition (PVD) to remove cobalt overburden. A high temperature anneal is then applied to reduce seams in the cobalt.
Due to the need for this high temperature anneal, voids in cobalt can migrate to the bottom of the features, and cause very high contact resistance or openings. There is thus a need for providing cobalt contacts (and other metallic contacts) that avoids the migration of the metallic material to the bottom of the features and thus lowers the contact resistance of the structure.